Traumatic brain injury (TBI) is a risk factor for the development of neurodegenerative diseases in which cognitive impairment is prominent, including Alzheimer?s disease and chronic traumatic encephalopathy (CTE). The high prevalence of mild TBI (mTBI) due to blast exposure in the recent conflicts in Iraq and Afghanistan puts veterans at increased risk of these disorders. Interestingly, male rats exposed to repetitive low-level blast exposures exhibit a chronic behavioral phenotype that includes elements of anxiety and post-traumatic stress disorder (PTSD)-related behavioral traits that are associated with hyperphosphorylated tau in brain at 10 months post-blast exposure as well as chronic elevation of the microtubule-binding protein stathmin 1. Alterations in these two key microtubule-binding proteins suggest that repetitive blast exposure may fundamentally alter microtubular networks, which could be of relevance to the development of neurodegenerative conditions such as CTE. These studies will determine the time course of the effects of low- level blast exposure on tau phosphorylation and processing using a cellular subfractionation strategy and biochemical analyses with a panel of antibodies against phosphorylated tau. Levels of other microtubule- associated proteins, including stathmin 1, together with the assembly status of microtubules will be examined over time. Blast-exposed rats also develop dendritic spine loss in the hippocampus. The time course of blast effects on dendritic spine density, dendritic spine number per unit length, spine type, and spine volume will be determined using quantitative stereology on spinophilin-immunostained sections and 3D reconstructed images of Lucifer Yellow-loaded neurons. Electron microscopy will be used to assess the ultrastructure of dendritic spines and microtubules. To test whether the chronic behavioral effects associated with repetitive low-level blast exposure are mechanistically related to effects on microtubule stability we will determine whether the microtubule stabilizing agent epothilone D can reverse the chronic behavioral effects that follow blast injury. It will also be determined whether behavioral changes persist or progress with aging following blast exposure and, in particular, whether age-related cognitive changes appear. Correlation of the molecular and morphological studies with the behavioral and cognitive tests will provide further insight into the mechanisms of blast-induced injury. A parallel set of studies will determine whether female rats develop a blast-related phenotype, which to date has only been studied in male rats. Collectively, the proposed studies will explore potential targets for the treatment of blast-induced brain injury in active duty military personnel and veterans affected by these potentially devastating injuries.